The present invention relates to a bookbinding apparatus that sets sheets with images formed thereon by an image forming apparatus or the like, into a bundle, applies an adhesive to a spine part of the sheet bundle, and binds the sheet bundle to a cover sheet for bookbinding, and in particular, to a bookbinding apparatus that joins a sheet bundle with a paste applied to a spine part thereof, to a central part of a cover sheet and folds back the cover sheet so that the sheet bundle is cased in the cover sheet for bookbinding.
Bookbinding apparatuses of this kind are widely used as terminal apparatuses for image forming systems such as printers or printing machines, automatic bookbinding systems that stack sheets with images formed thereon, in order of pages, set the sheets into a bundle, apply a paste to an end surface of the bundle, and bind the bundle to a cover sheet, or bookbinding apparatuses that set print sheets supplied through a sheet feeding port and bind the set sheets to a cover sheet. In particular, in connection with on-demand printing such as electronic publishing, a recently known system simultaneously executes a printing process and a bookbinding process by printing predetermined documents while automatically binding the documents together to produce booklets.
For example, Japanese Patent Publication Laid-Open No. 2004-209869 discloses, like the system described above, an apparatus configuration that automatically binds sheets output by an image forming system, into a book. According to Japanese Patent Publication Laid-Open No. 2004-209869, the apparatus receives sheets output by the image forming system through a sheet discharging port, guides the sheets to a sheet carry-in path, and collects the sheets on a loading tray provided downstream of the path. The apparatus then swivels the sheet bundle collected on the tray in a horizontal posture through 90° and guides the bundle in a vertical posture to a pasting device for an applying process. Then, the sheet bundle with a paste applied thereto and a cover sheet supplied by the image forming system or an inserter apparatus are folded and bound together.
A conventionally known bookbinding method used for such a bookbinding system is casing-in in which a sheet bundle with a paste applied to a spine part thereof is joined to the center of a cover sheet carried in from a direction orthogonal to the sheet bundle and in which the cover sheet is then folded to form the sheets into a booklet. In this case, the cover sheet having the sheet bundle joined to the center thereof is pressed by a lateral pair of back folding blocks to form a spine part. Accordingly, the system adopts a structure in which the lateral pair of back folding blocks is shaped like a press tool and in which the back folding blocks each lying at a standby position laterally away from a central back folding position as a reference move closer to each other to fold the spine part of the cover sheet at the central back folding position.
Japanese Patent Publication Laid-Open No. 2005-104063 discloses that after a cover sheet is bound to a sheet bundle with an adhesive applied thereto, a cooling time during which the adhesive is cooled for solidification is adjusted depending on the thickness of the sheet bundle. According to Japanese Patent Publication Laid-Open No. 2005-104063, the cooling time to be adjusted corresponds to the time required to execute a bookbinding step and a subsequent cutting step.
When a hot melt adhesive is applied to the spine part of the sheet bundle, which is then joined to the cover sheet in inverse T shape, and the spine part of the cover sheet is then folded back by the press member, as described above, the following problem may occur. If the adhesive layer is unnecessarily thick, then during back folding pressing, an excess portion of the adhesive may leak from opposite shoulders (k1 and k2 in FIGS. 11 (a) and 11(b)) of the spine cover toward the back cover. This is shown in FIG. 11(a). The inside of the front cover of the cover sheet may be mistakenly attached to the first page of the saddle-stitched sheets (print sheets), and the inside of the back cover may be mistakenly attached to the end page of the saddle-stitched sheets. Furthermore, if the adhesive layer is unnecessarily thin, then as shown in FIG. 11(b), the cover sheet and the saddle-stitched sheets may disadvantageously not be bonded together at the back folding shoulders (k1 and k2), resulting in degraded bookbinding quality or missing pages.
To solve these problems, the amount of adhesive to be applied by paste applying means is adjusted depending on the thickness of the sheet bundle so as to form an appropriate adhesive layer on the bundled saddle-stitched sheets. In spite of the adjustment of the thickness of the adhesive layer, the adhesive may leak from the back folding shoulders or an insufficient amount of adhesive may be applied to the shoulders. In particular, a large amount of leaking adhesive may wrinkle the spine cover or distort back folding edges, degrading the bookbinding quality. The insufficient adhesion of the shoulders may cause a serious problem such as missing pages.
The inventor has thus found the following with respect to the leakage of the adhesive from the back folding shoulders and insufficient adhesion: in connection with the relationship between the back folding press member for embossing and a plate member backing up the cover sheet, a thicker cover sheet is likely to result in the leakage of the adhesive from the back folding shoulders and a thinner cover sheet is likely to result in the insufficient adhesion of the shoulders.
The first object of the present invention is to provide a bookbinding apparatus that, when bundled sheets are cased in a cover sheet for bookbinding, prevents the possible leakage of an adhesive from shoulders of a spine cover or possible insufficient adhesion.
The second object of the present invention is to provide a bookbinding apparatus that, when the cover sheet is folded back, prevents folds in the spine cover from being distorted or wrinkled, and an image forming system comprising the bookbinding apparatus.